1. Field of the Invention
The present invention relates to a vehicular electronic key system that is applied to controlling a vehicle such as a car, an automobile, etc., and more particularly, it relates to a new technique for an on-board device that detects the presence or absence of a portable device.
2. Description of the Related Art
In recent years, a variety of advanced techniques have been proposed for vehicular electronic key systems that control door locking, engine starting, etc., of a vehicle through an on-board device which is controlled by a portable device operated by a user of the vehicle.
Also, there has been proposed a technique that verifies the existence of a portable device through communication thereto from an on-board device during the time when a vehicle is standing still or travelling, and generates, in case of the absence of the portable device, an alarm or warning so as to inform a user of the loss or missing of the portable device thereby to prompt the user to look for it (see, for example, a first patent document (Japanese patent application laid-open No. 2004-114860)).
In the known vehicular electronic key system, a procedure of specifying the undetected state of a portable device is as follows:
(1) The portable device is detected at each fixed time (e.g., 10 seconds).
(2) A detection operation is executed at a fixed time period or interval from a first undetection of the portable device.
(3) The number of times or frequency of continuous or successive undetections of the portable device is counted so that when a predetermined frequency is reached, a warning is generated.
(4) If the vehicle is travelling after the generation of the warning, the user returns to a location where the portable device might be lost, and looks for the portable device.
In the known vehicular electronic key system, the undetected state of the portable device is merely warned, so the user can recognize that the portable device has become in the undetected state, but there has been a problem that in case where the vehicle is travelling, it is impossible to recognize in what time (hour) band or in what place (area) the undetected state of the portable device occurred, and to specifically know where the portable device was lost.
In addition, there has also been a problem that even when the vehicle is standing still or stopping, by merely generating an alarm or warning from the on-board device, it is impossible to recognize what time the communication with the portable device was disrupted or broken off.
Moreover, in case where the presence or absence of the portable device is detected during travel of the vehicle, the detection of the portable device is tried to be repeated at fixed time intervals after it has been determined for the first time that the portable device is in an undetected state, so that the start of warning is finally decided or fixed, an alarm or warning is generated. As a result, the time point of generation of such an alarm or warning becomes after the vehicle has moved away from the point (i.e., the first undetected point or location) where the undetected state of the portable device was generated for first time, so there arises a problem that the range in which the undetected point of the portable device is to be specified increases too much depending upon the detection time interval and the vehicle speed, thus resulting in difficulty for the user to specify the undetected point.
Further, in order to generate an alarm or warning in a place near the undetected point of the portable device thereby to reduce the undetected point specifying range, it can be considered that the detection period of the portable device is set shorter, but in this case, there arises a further problem that mutual communication between the on-board device and the portable device becomes more frequent, so the battery consumption of the portable device becomes more intense, thus impairing the original or intrinsic function of the vehicular electronic key system. As a result, such a scheme is not practical.